Implantable medical devices are commonly used today to treat patients suffering from various ailments. After implant of an implantable device for electric stimulation, such as pacemakers or Deep Brain Stimulation (DBS) devices, the device and surrounding tissue may be heated during scanning of the patient and device by e.g. Magnetic Resonance Imaging (MRI) scanning. The human tissue, in particular brain tissue, is sensitive to temperature raises; the maximum allowed temperature increase of brain tissue is 1° C. in that further temperature increases may have profound, negative effects on single neuron and neuronal network function. Therefore it is of concern to minimize heating effects at and around an implanted medical device due to induced currents near the medical device during MRI scanning.
It might seem natural to choose high resistive materials throughout the implantable device, ideally with the same specific resistance as the human tissue. However, this typically would require much more power to obtain the same tissue stimulating signals at the end of the probe compared to probes using low resistive materials. Consequently, either unacceptable large batteries or unacceptable short battery life time would result.
U.S. Pat. No. 4,353,360 describes an electrode for a body implantable lead having a semiconductor surface for coupling of electrical signals to the body tissue. The electrode comprises several materials of differing conductivities, arranged in layers such that the material having the lowest conductivity is in direct contact with the body tissue.
An improved probe for implantable medical devices with minimized heating effect would be advantageous. Moreover, a probe which after implant and during MRI scanning would produce a reduced current density within the human tissue surrounding the probe of the implanted device, compared to known probes for implantable medical devices, would be advantageous.